Recent years have seen a great deal of research into Vehicle-to-Vehicle (V2V) and Vehicle-to-Infrastructure (V2I) communications, which will contribute to advances in driving support systems. In contrast to V2I communications, V2V communications offer the advantage of not requiring infrastructure, but introduction of such systems is not expected to be effective unless there is sufficient penetration by On-Board Units (OBUs). For that reason, it is essential to determine what extent of penetration should be encouraged in the initial stage in order to attain effectiveness. Therefore, we focus on the fact that even though Large Vehicles (LVs) such as large commercial freight carriers are large and tall, and are obstacles blocking V2V communications from the viewpoint of Small Vehicles (SVs), antennas on LVs could also be used to relay communications, thereby facilitating the success of such systems.
  This paper presents experiment s simulating traffic environment s consisting of mixed LVs and SVs, and examined how data V2V communication distribution rates varied with changes of the percentage of vehicles equipped with OBUs. Through the simulation experiments, by causing actively penetrate LVs, it revealed that the reception rate of SVs can be improved, and clarified some guidelines for policies that could encourage wider usage.